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L. O. HOWARD. F-ntomologiM and ( h.rf „MW.u. 




war -it 



L. O. Howard, Entomologist and Chief of Bureau. 

O. L. Marlatt, Entomologist and Acting Chief in Absence of Chief. 

R. S. Clifton, Executive Assistant. 

W. F. Tastet, Chief Clerk. 

F. H. Ghittendew', in charge of truck crop and ston d product insect investigations. 
A. D. Hopkins, in charge of forest insect investigations. 
W. 1). Hunter, in charge of southern field crop insect investigations. 
F. M. YVkisster, in charge of cereal and forage insect investigations. 
A. L. Quaintance, in charge of deciduous fruit insect investigations. 
E. F. Phillips, in charge of bee culture. 

D. M. Rogers, in charge of preventing spread of mollis, /,>/,/ work. 
ROLLA P. CURRIE, Ml charge of libra))/. 

ADDITIONAL COPIES of this publication 
Xjl may he procured from the Superintend- 
ent of Documents, Government Printing 
Office, Washington, D. C , at 5 cents per copy 

Circular No. 163. imutA NoTemtx 

Doited States Department of Agriculture, 

L O HOWARD, Entomologist and Chief of Bureau. 

Bj I.. « >. How led and '>'. ll. Popi si 

Hydrocyanic-acid gas ia one of the most effecl ive remedies known 
against various classes of insects. For more than 20 years it 
baa been the principal means of controlling scale insects <>n citrus 
in California and is do^k in general use for the disinfection of 
all deciduous nursery stock and other plant material l'<u- shipment, 
ami is one of the m< »-t effective methods of i-i < 1» I i 1 1 ir greenhouses and 
cold frames of plant-lice, thrips, white flies, and various scale pots 
which infesl plants grown under glass. 1 It has also become a stand- 
ard remedy against the M< diterranean flour moth and other mill and 
grain insed 

It has been fully demonstrated that this gas, which i< very deadly 
to all forms of animal life. i-. under proper precautions, an excellent 
remedy for household ii sects. Probably it- lit-' use for this purpose 
a June of 1898, by Mr. C. L. Marlatt, of this bureau, against book 
lice in the residence of an employee of the I department <>( Agriculture, 
using the cyanid first at the ordinary strength employed on fruit 
n double, and finally quadruple the strength. The book lice 
came from recently introduced leather-covered furniture, the cover- 
ing of which was so tightly fastened a- to In- almost, if not quite. 
impervious to the gas, and the treatment was only partially succes- 
ful. Another early use of this ira- for household insects was in 1899 
iii San Francisco by the late Alexander Craw, then Chief Qua rani me 
Officer of the Board of I lorticulture. In this case it was used against 
bedbugs ami in very -mall proportions. Two and one-half fluid 
ounces of commercial sulphuric acid and -j\ ounce- 98 percent cyanid 
of potass i u m were used in a house of several rooms, each containing 
•boat 2,250 cubic feet of -pace. The rooms were closed for two 
hour-, then well aired. The operation .\a- apparently successful. 

IF rrn.-r-' Bui' 
letln ITS. 

• Refer to Clrcnlu 118, B ( tttenden. 



Perfectly successful experiments were made during the summer of 
1901 by Mr. W. R. Bent tie, of the Department of Agriculture, and by 
Mr. A. H. Kirkland, at Boston, Mass. Mr. Beattie's experiments 
were against cockroaches and Mr. Kirkland's in one case against 
fleas and in other against clothes moths. 

During the period between 1901 and 1907 hydrocyanic-acid gas 
was used in practical work by several members of the Bureau of 
Entomology, under the direction of Mr. Marlatt, many residences 
and public buildings, schools, churches, and stores being fumigated 
with practically uniform success. Indeed the efficiency shown by 
this gas in the control of household insects lias led to its adoption as 
a standard remedy for these pests, and it has since been adopted for 
the destruction of insects affecting stored products, especially for the 
control of the Mediterranean flour moth (Ephestio JcuehnieUa Zell.) 
in mills and warehouses. For this purpose it has proven extremely 
effective, having been used under the direction of agents of this 
bureau for the destruction of the flour moth in over 100 mills with 
excellent results. 

Some entomologists recommend as a substitute for hydrocyanic- 
acid gas a substance which has been more or less effectively used, viz, 
carbon bisulphid. The great danger in the use of this latter sub- 
stance, however, from its extreme inflammability and the explosive- 
ness of its vapor when confined, renders it perhaps less available and 
more than counteracts the danger to human beings from the use of 
the hydrocyanic-acid gas. It has, moreover, been found that the 
hydrocyanic-acid gas is much more effective for the control of all 
groups of household insects, with the exception of the beetles, than 
is the other fumigant. 

Entomologists have long noticed that insects vary greatly in their 
susceptibility to cyanic! fumes. The ordinary killing bottle used in 
making collections contains cyanid of potassium covered with plaster 
of Paris, which the fumes of the cyanid penetrate. Certain weevils, 
and especially such weevils as Lixus and Sphenophorus and other 
hard-bodied forms, will frequently be left overnight in a cyanid 
bottle and recover after being removed. It has been noticed also that 
in greenhouses certain insects recover. The experience gained, 
however, indicates that the use of hydrocyanic-acid gas in houses is 
successful against cockroaches, bedbugs, fleas, clothes moths, ants. 
white ants, house flies, and other soft-bodied insects; and as these 
constitute the majority of the household pests, the use of the gas 
must now be considered a standard remedy. Moreover, rats and mice 
are also' killed by its use, and it fortunately has the effect of first 
causing these animals to rush out from their holes into the open, so 
that the subsequent annoyance of dead mice in walls and under floor- 
ings is not experienced. 


DIBI I riONfl I OH l -i . 

Much experience indicates thai in order to destroy the household 
insects mentioned, l fluid ounce of commercial sulphuric acid (ab< ul 
1.84 sp. gr., 66 Bauml) diluted with •"> fluid ounces of water, i<> 
increase the hulk of the liquid and insure complete chemical action, 
and 1 ounce of high grade (98 percent) cyanid of potassium, must 
!>«■ u-«-«l for everj 100 cubic feel of space. The formula per hundred 
cubic feet, therefore, is as follows: 

Potassium cyanid (08 percent) avoirdupois ounce i 

('.■ sulphuric acid fluid ounce i 

Water fluid ounces 3 

For loosely constructed frame houses the above amounts may be 
doubled per hundfed cubic feet. The cyanid costs about !<■ cents a 
pound and the sulphuric acid (thick or more sirupy commercial 
brand) about 1 cents a pound. 

The purity of the cyanid < if potash and sulphuric acid to the degree 
indicated is essentia] i" the success of the fumigation. Potassium 
cyanid may be obtained in various " technical " grades, ranging be- 
tween I" per cent and 98 to 100 per ceml actual cyanid, the remainder 
being an ineii salt, usually -odium carbonate or -odium chlorid, which 
is of no value in fumigation and in the case i f -odium chlorid is a 
positive detriment, as this substance, acted upon by sulphuric acid, 
produces hydrochloric acid, which decomposes the hydrocyanic-acid 
gas. In cases of extreme adulteration as much as 60 per cent of the 
fumigant may be decomposed in this manner, resulting in inferior 
effectiveness and tending to tarnish polished metal surfaces exposed 
to the gas. I f chemically pure cyanid is used little tarnishing results. 

Many of the manufacturers of cyanid place on the market a " -•>- 
called potassium cyanid" which consists of sodium cyanid adul- 
terated with sodium chlorid. The chemically pure sodium cyanid 
liberates 33 per cent more hydrocyanic-acid n-.t- than does the pure 
potassium cyanid, so thai to avoid adulterated chemical- it i- well 
to secure the -"-called " 133 per cent sodium cyanid " for best results. 
In the use of this chemical a correspondingly greater amount of the 
acid ia necessary for the complete exhaustion < f the cyanid. 1 

Before performing the operation the house must be vacated. It is 
not necessary to remove any of the furniture or household belongings 
unless of polished nickel i r brass, which may tarnish a little. Liquid 
or moist food-, as milk, meat-, or other larder supplies that are not 
dry and illicit absorb the i_ r a-. should be removed from the house. All 
lire- should he put out: for while the gas will not burn under ordi- 
nary condition-;, it i.- a- well to take no risks. 

an Cyaald for Fumigation Purposes," i>\ i: s Wogltun (BnL 
80, rt. II. Bureau ..f Entomology, 1»11). Mr Woginm'i studies ol sodium cyanid bare 
reference eapedali] t" it- ose in the fumigation <>f citrus orchards 


The cubic contents of each room on each floor should be carefully 
computed and a tabular statement, .such as that gives below, pre- 
pared, designating for each floor and the different rooms the capacity 
and the amount of water, acid, and cyanid needed. 

Table designating rooms, capacity, and amounts <>i chemicals. 



Cubic feet. 



Cyanid . 



i 7, 000 



' 5, 500 




Fl. <>:. 



















A vd. oz. 




Mid. lie 





Mi. 1. lie 






Middle . 













1 The charges for thes? rooms should be halved and Bet off in I wo vessels. 

The house is prepared for treatment by seeing that all the win- 
dows are closed and calked, if of loose construction, with wet paper 
or cotton batting tucked tightly into the crevices. Gummed paper 
strips are obtainable for this purpose, which may be pasted over the 
crevices in the doors and windows, making the room practically 
gas-tight. As the building must be aired by opening the windows 
from the outside, those selected to be opened should be examined to 
see that they pull down easily, and if too high to be reached from the 
ground should be provided with strong cords reaching to the ground 
that they may be easily opened from below. They should be opened 
before closing for the last time, in order to test the strength of the 
cord and should not be pasted up or calked. The fireplace flues in 
the different rooms should be stuffed with paper and the register- 
closed. Carpets and rugs, where possible, should be cleared away 
from the floor to prevent their being burned should the acid spatter 
or boil over. 

For generators, stoneware or crockery jars Inning a capacity of 4 
gallons are preferable and may be used with a charge of up to 3 
pounds of cyanid. One of these vessels should be placed in each 
room, with the exception of large rooms requiring a charge of more 
than 3 pounds of cyanid, when the charge may be divided. One 
vessel will suffice for each 3,000 or 4.000 cubic feet, preferably the 
former amount. Under each of these vessels a rather thick carpeting 
of old newspapers should be placed, or a larger vessel, and care must 
be exercised to see that none of the vessels is cracked, <>n account of 


the danger of breakage from the heal generated bj the pro 
1)(H'|) vessels are more satisfacti ry for the experiment than the wash 
basins often used, 1 >ut the latter are always available and will serve 
the purpose. Deeper vessels i_ r i\c greater depth to the water and 
acid and accelerate the chemical action, and there is less danger of 
Bpattering. Whenever the room is of such size thai much more than 
.*{ pounds of cyanid musl l>c employed for it, it is perhaps better t<> 
make two charges of half size for such room. 

n:o< ESS 01 ii M n. \ HON. 

In the process of generating the gas the water may I"' measured 
in a glass beaker indicating ounces, i r for 'onvenience in a pinl cup, 
and poured into the generators. The acid, measured in the same 
receptacle, is then slowly and gently poured into the water lo av< id 
splashing or boiling. For all ordinary purposes 1 pint of the arid 
and :'> pints of water arc sufficient f< r each pound of cyanid. T/u 
acid should never bt placed in tin gen \ as advised by 

some writers, since experience shows thai this is dangerous, spatter- 
ing being almosl certain to follow. When the arid is poured into 
the water in the jar an ebullition of vapor sometimes arises. Con- 
siderable heat is also developed by the addition of the acid. 

When the cyanid of potash is finally dropped into the combined 
acid and water mixture an ebullition or bubbling also take- place 
similar to that which is produced by a red lot iron dipped into cold 
water. Ne\t is given off the hydrocyanic-acid gas, the mosi poi- 
Bonous gas in common use. It is colorless and has an odor which has 
been likened to thai of peach kernel-. II' the fumes are inhaled they 
arc almosl certain to prove fatal; hence the necessity of extreme care 
and the advisability of two intelligent operators in this work. It i> 
even advisable, especially when the firsl fumigation is undertaken, 
that one who has had experience with this method of fumigation be 
-it to give direction-. The odor i- decidedly metallic, like thai 
produced by striking two pieces of metal together, or of metal against 

The measuring and preparation of the water and acid in the fumi- 
gating jars should be undertaken in a room with a tile or concrete 
tloor if possible, as the -none; acid used is apt to injure wooden floors 
Or carpets should .-pillniij: occur. The jar- may then be distributed 
to the different rooms and a bag containing the requisite cyanid 

placed by the side of each. 

The house is now in readiness to be fumigated. Coat- and hats and 
everything needed outside musl be removed, and preferably two per- 
sons should then go to the top of the house, taking different room- on 
the same floor to expedite the process, and place the hair- containing 
the cyanid erentlv into the vessels to receive them. The chemical 


action will begin at once, but the gas will not rise to any extent for a 
few seconds or a quarter of a minute, and there is ample time to leave 
the room quickly without danger of breathing the gas. Having 
finished the garret or top floor, the operators should pass rapidly to 
the next, and so on to the basement, making their exit through the 
lower door to the street. 

Hydrocyanic-acid gas is lighter than air, and consequently rises; 
therefore the operation must be begun at the top of the house. 

The house should be locked from the outside and, if necessary, a 
warning sign put up to caution against entrance. 

The preparation of the different rooms, getting their cubic contents, 
fixing the vessels, and preparing the charges, in a house of the size 
indicated in the table given above, will take from two to three hours, 
and this much time must be allowed for. The house should remain 
closed, for the gas to become fully generated and do its work, for 4 
to (') hours — preferably, however, and to get the greatest efficiency, 24 
hours at least. 

Better results are claimed for a warm temperature, say 70° F. or 
above, than in a temperature as low as .">0° F. or below. Under 50° 
most insects become torpid and the effective action of the chemical 
will be diminished, especially in very low temperatures. 

At the close of the operation the doors may be opened and the 
windows lowered or opened from the outside, and after an hour's 
airing the house may be entered if no strong odor of gas is detected, 
and opened up even more thoroughly, if possible, to allow a complete 
airing for several hours. The house should not be reinhabited until 
all traces of the odor of the gas have disappeared. This odor, as 
stated before, has been compared to that of peach kernels. 

The contents of the generating jars should be poured into the 
sewer trap or disposed of in some place where they will not be a 
source of danger, and the jars thoroughly cleaned. 


In the use of hydrocyanic-acid gas for household fumigation it 
must not be lost sight of for a single instant that one is dealing with 
one of the most poisonous substances known, and that the accidental 
eating of a small portion of cyanid will necessarily be fatal, and that 
the inhalation of a few breaths of the gas will asphyxiate, and, if 
rescue be not prompt, also have a fatal termination. Tt is much 
better, therefore, if fumigation be contemplated, to put the work in 
the hands of some one who has had experience, if such a person be 
available; if not. to consider carefully all the recommendations and 
precautions in this circular and become thoroughly familiarized with 
them before undertaking the experiment. 


While the writer thus strongly emphasizes the dang ind even 

htal qualities of this gas when breathed bj human beings, it is 
worthy of remark thai in the thousands of operations which have 
been carried on with this gas in the course of its various applicatioi 
i„ different parts of the world, onlj two ca es of fatal accidents to 
human beings have been recorded. These were due to extreme car. 
lessness in its use. In i ne case the operator wenl back into the hou • 
after having dr< pped the bags and closed the building for some time. 
The abundant experience which has been gained by the differed 
members of the f< rce of this office and manj others in the fumigation 
of dwelling houses has demonstrated thai all dang i dy over- 

come by care in conducting the operation, and in all the house-fumi- 
gation work which has been done during the last five years no accid. 

has occurred, excepl in on ■ two instances the burning ol rugs 

i„ attempting to set off charges in too small vessels and a case oi 
headache where a few whiffs of much diluted gas had been acci- 
dentally breathed. 

I, follows, from what we have jusl said, that there may be danger 
from fumigating one hoUse in a ro* of houses separated only by 
party walls, the other house being inhabited. Unnoticed cracks in a 
wall would admit the poisono neighboring house. In 

Such ;. case a householder musl consult his neighbors. In isolated 
houses, however, with the precautions indicated, the operation will be 

lfe one The fad that birds resting on the ridge of fumigati 
houses have been killed by the ascending fumes indicates also that 
where the house to be operated upon immediately adjoins a higher 
Structure to which the gas may possibly gain entrance there may be 
some danger to the occupants of the higher structure. 

It is undesirable to fumigate single apartments or rooms in build- 
ings and this should only be attempted when the whole building can 
be vacated during the operation. In case of contiguous houses ol 
loose construction an arrangement should be made so thai the adjoin- 
ing houses also may be < acated during fumigation. 

In handling the acid greal care should be used in pouring it I 
the bottle and in putting il into the vessels to avoid spattering on 
the hands or face, since il will burn rapidly through the skin, and 
should it spatter into the eyes would cause serious inflammation, or 
it - on the clothing it would burn a hole in the garment - Id a 
drop fly to the hands or face, bathe the pari promptly and freely in 
water and the same also for garments or the carpet. It is further 
dosin.blc to have at hand a bottle of water to neutralize 
the acid should it spatter on clothing. 

The handling of the dry cyanid is not accompanied by any dai 
if there be no open wound on the hand, bul it is advisable to wear 
an old pan- of gloves in breaking up the cyanid and putting it in 


the sacks, these gloves to be afterwards burned. The fact that the 
cyanid has a superfica] resemblance to sugar adds to the danger of 
keeping it about the premises, and it is much better to at once deeply 
bury or throw down the sewer trap any left-over cyanid. 


The general directions for treatment may be briefly summarized 

as follows : 

(1) Prepare tabular statement designating room capacity and 
amount of chemicals for each compartment, and secure the chemicals 
and vessels for generating the gas. 

(2) Arrange for the opening of doors and windows from the out- 
side at the conclusion of the fumigation, and close all register-, fire- 
places, and other openings. Do necessary calking and remove carpets 
and rugs and moist food material and any metallic objects which are 
likely to be tarnished. 

(3) Place the generating vessels in each room with a thick carpet- 
ing of old newspapers under each. 

(4) Break up the cyanid out of doors and place it in thin paper 
sacks containing a pound or a half pound each, suited to the amounts 
to be used in the different rooms. 

(5) Measure into each of the generating jars the proper amount of 
water, and afterwards add the acid slowly in the proper amount to 
each of the jars. 

(6) Take the cyanid in baa- in a basket and place the bags to the 
proper amount alongside of the generating jars in each room. 

(7) Start at the top of the house and place the cyanid gently, so 
a- not to spatter, into each jar. and quickly leave the room. Ajs 
soon as the upper floor is finished go to the next lower, and pass in 
tli is manner from floor to floor until the basement is reached and 
exit is made through the lower door. If two persons work together 
in this operation they should both be on the same floor together, 
taking different rooms. 

(8) The following day. or after the completion of the fumigation, 
open the windows and doors from the outside, and let the house 
ventilate for an hour before entering it. 

(9) After the house is thoroughly ventilated and the odor of the 
gas has disappeared, the jars should be emptied in a safe place, pref- 
erably through the sewer trap, and thoroughly and repeatedly washed 
before being used for any household purpose. 

Approved : 

James Wilson, 

Secretary of Agricultun . 

Washington, D. C, Octdbt r ..'/. 191 1. 



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